Energy-use efficiency of organic and conventional plant production systems in Germany

Sustainable and efficient energy use in agriculture helps tackle climate change by reducing fossil energy use. We evaluated German farming systems by analysing energy input and output. Data from 30 organic and 30 conventional farms (12 arable, 18 dairy farms each) between 2009 and 2011 was used. Energy input, output, and the influence of farm type, farm structure, and management intensity on energy-use efficiency (EUE) were analysed for crop production using the farm management system REPRO. Conventional farms (CF) always had higher energy input. The energy input for organic farms (OF) was 7.2 GJ ha−1 and for CF 14.0 GJ ha−1. The energy output of CF was also higher. Reductions were higher in energy input than in energy output. In 73.3% of the farm pairs, OF were more energy efficient than CF. The EUE was comparable with CF on 10% of OF and for 16.7% of CF the EUE was higher suggesting better fossil energy utilization. EUE can be increased when reducing fossil energy inputs through more efficient machinery, reduction of agrochemicals, precision farming, the use of renewable energy or energy retention, and by increasing yields. A reduction of inputs is urgently required to lower the (political) dependence on fossil energy.

Indirect energy input (Ei) Seed + mineral and organic fertilizers + pesticides + machines GJ ha -1 yr -1 Energy input (E) E = Ed + Ei GJ ha -1 yr -1 Energy output (EO) Energy in the harvested biomass (main product + by-product) -energy in the seed GJ ha -1 yr -1 Energy use efficiency (EUE) EUE = EO / E --Energy-use efficiency is defined as energy output in relation to energy input.A definition of the energetic parameters and their calculation is given in Table 1.
The energetic analysis was done with a process analysis.This is a more mechanistic technique, attempting to trace all fossil energy inputs into an agricultural system based on physical material flows, and is suitable for calculating energy balance, analyzing energy-use efficiency, and comparing and improving farming systems (Hülsbergen et al., 2001;Küstermann et al., 2008;Alluvine et al., 2011;Rossner et al., 2014;Jankowski et al., 2015).We analyzed the plant production of farming systems at field level.Therefore, for organic mixed farming system, only the crop production subsystem was included but not the animal production subsystem.
The system inputs and outputs and system boundary are shown in  plant protection products, machinery, etc. (Hülsbergen et al., 2001).The packaging and transportation of these materials are also parts of the indirect energy.
To include the input of energy associated with the manufacture, packaging, and transportation of production means in terms of primary energy input, energy equivalents were used (Hülsbergen et al., 2001).These equivalents are the widely-used values for representing the mean German conditions relevant and modern technologies, and hence are appropriate for this study (Lin et al. 2016).
Energy equivalents were used to express the input of energy associated with the manufacture of production means in terms of primary energy input.There is an enormous variation in energy equivalents reported in the literature.This is the result of differences in the methods of calculation and in the spatial and temporal system boundaries.Energy equivalents are not fixed once and for all.
They must be adapted to local conditions (e.g.transport distances) and to changes in the manufacture of production means.Special emphasis must be put on the energy equivalents of fertilizers, because the rate of fertilizer application has a particularly strong effect on the energy input (Hülsbergen et al. 2002).Energy output was calculated on the basis of DM yields and the gross energy content (calorific values) of products.We analyzed the harvested products (e.g.wheat, GCA) independent of the use of these products.However, the non-harvested biomass (e.g.straw, leaves, residues, and green manure) are not accounted in this study (see Table 1).Calorific values were derived from the product quality (the content of protein, fat, fiber, and N-free extracts, see Hülsbergen et al. (2001)).
Figure xy.The energy inputs considered both direct energy and indirect energy.Direct energy is the energy used on the farm (fuel, electricity), and indirect energy is energy used outside of the farm for the manufacture of fertilizers,